The present invention is directed to the field of low pressure chemical vapor deposition of silicon nitride films using bis(tertiarybutylamino)silane, a novel organosilicon source material for silicon nitride.
In the fabrication of semiconductor devices, a thin passive layer of a chemically inert dielectric material such as, silicon nitride (Si.sub.3 N.sub.4) is essential. Thin layers of silicon nitride function as diffusion masks, oxidation barriers, trench isolation, intermetallic dielectric material with high dielectric breakdown voltages and passivation layers. Many other applications of silicon nitride coatings in the fabrication of semiconductor devices are reported elsewhere, see Semiconductor and Process technology handbook, edited by Gary E. McGuire, Noyes Publication, New Jersey, (1988), pp 289-301; and Silicon Processing for the VLSI ERA, Wolf, Stanley, and Talbert, Richard N., Lattice Press, Sunset Beach, Calif. (1990), pp 20-22, 327-330.
The present semiconductor industry standard silicon nitride growth method is by low pressure chemical vapor deposition in a hot wall reactor at &gt;750.degree. C. using dichlorosilane and ammonia.
Deposition of silicon nitride over large numbers of silicon wafers has been accomplished using many precursors. The low pressure chemical vapor deposition (LPCVD) using dichlorosilane and ammonia requires deposition temperatures greater than 750.degree. C. to obtain reasonable growth rates and uniformities. Higher deposition temperatures are typically employed to get the best film properties. There are several drawbacks in these processes and some of these are as follows:
i) Deposition under 850.degree. C. gives poor hazy films with chlorine and particle contamination; PA1 ii) Silane and dichlorosilane are pyrophoric, toxic compressed gases; PA1 iii) Films formed from dichlorosilane result in the formation of less uniform films; and PA1 iv) Films from dichlorosilane have contaminants, such as chlorine and ammonium chloride, which are formed as byproducts. PA1 1) They contain N-methyl groups, the methyl groups tend to migrate to the silicon surface readily and contaminate the films with carbon during a CVD process. In order to reduce the amount of carbon, the process involves high temperatures (&gt;700) and high ammonia ratios (&gt;10:1). With increased ammonia ratios the deposition rates dramatically reduce due to reactant depletion. PA1 2) They do not contain NH bonding and they do not involve secondary silanes. PA1 3) At lower temperatures the deposition rates and uniformities are very poor (&gt;5%). PA1 a) heating a substrate to a temperature in the range of approximately 500.degree.-800.degree. C. in said zone; PA1 b) maintaining the substrate in a vacuum at a pressure in the range of approximately 20 mTorr-2 Torr in said zone; PA1 c) introducing into said zone ammonia and a silane of the formula: (t-C.sub.4 H.sub.9 NH).sub.2 SiH.sub.2 ; and PA1 d) maintaining the conditions of a) through c) sufficient to cause a film of silicon nitride to deposit on the substrate.
Japanese Patent 6-132284 describes deposition of silicon nitride using organosilanes with a general formula (R.sub.1 R.sub.2 N).sub.n SiH.sub.4-n (where R.sub.1 and R.sub.2 range from H--, CH.sub.3 --, C.sub.2 H.sub.5 --C.sub.3 H.sub.7 --, C.sub.4 H.sub.9 --) by a plasma enhanced chemical vapor deposition and thermal chemical vapor deposition in the presence of ammonia or nitrogen. The precursors described here are tertiary amines and do not contain NH bonding as in the case of the present invention. The deposition experiments were carried out in a single wafer reactor at 400.degree. C. at high pressures of 80-100 Torr. The Si:N ratios in these films were 0.9 (Si:N ratios in Si.sub.3 N.sub.4 films is 0.75) with hydrogen content in the deposited films. The butyl radical is in the form of isobutyl.
Sorita et al., J. Electro. Chem. Soc., Vol 141, No 12, (1994), pp 3505-3511, describe deposition of silicon nitride using dichlorosilane and ammonia using a LPCVD process. The major products in this process are aminochlorosilane, silicon nitride and ammonium chloride. Formation of ammonium chloride is a major drawback of using Si--Cl containing precursors. The formation of ammonium chloride leads to particle formation and deposition of ammonium chloride at the backend of the tube and in the plumbing lines and the pumping system. Processes which contain chlorine in the precursors result in NH.sub.4 Cl formation. These processes require frequent cleaning and result in large down time of the reactors.
B. A. Scott, J. M. Martnez-Duart, D. B. Beach, T. N. Nguyen, R. D. Estes and R. G. Schad., Chemtronics, 1989, Vol 4, pp 230-234., report deposition of silicon nitride using silane and ammonia by LPCVD in the temperature region of 250.degree.-400.degree. C. Silane is a pyrophoric gas and is difficult to control for the deposition of clean silicon nitride due to partial gas phase reaction.
J. M. Grow, R. A. Levy, X. Fan and M. Bhaskaran, Materials Letters, 23, (1995), pp 187-193, describe deposition of silicon nitride using ditertiarybutylsilane and ammonia by LPCVD process in the temperature range of 600.degree.-700.degree. C. The deposited silicon nitride films were contaminated with carbon impurities (10 atomic %). This is mainly due to the presence of direct Si--C bonds in the precursor.
A. K. Hochberg and D. L. O'Meara, Mat. Res. Soc. Symp. Proc,. Vol. 204, (1991), pp 509-514, report deposition of silicon nitride and silicon oxynitride by using diethylsilane with ammonia and nitric oxide by LPCVD. The deposition was carried out in the temperature range of 650.degree. C. to 700.degree. C. The deposition is limited to deposition at 650.degree. C. and the deposition rate drops to below 4 .ANG./min at lower temperatures. In the LPCVD process, precursors which contain direct Si--C carbon bonds result in carbon contamination in the films. Carbon free deposition requires greater than 5:1 NH.sub.3 to precursor ratios. At lower ammonia concentrations, the films were found to contain carbon. Diethylsilane+ammonia processes typically require covered boats or temperature ramping to improve uniformities across the wafers.
U.S. Pat. No. 5,234,869 and R. G. Gordon and D. M. Hoffman, Chem. Mater., Vol. 2, (1990), pp 482-484 disclose other attempts to reduce the amount of carbon involved aminosilanes, such as tetrakis(dimethylamino)silane. The temperature of deposition is in the range of 300.degree.-1000.degree. C. with pressures in the range of 1 mTorr-10 Torr. The presence of direct Si--N bonds and the absence of Si--C bonds were expected to give lower carbon concentrations in the films. However, there are three main disadvantages with precursors of this class.
The prior art has attempted to produce silicon nitride films at low temperatures, at high deposition rates and low hydrogen and carbon contamination. However, the prior art has not been successful in achieving all these goals simultaneously with one silicon precursor. The present invention has overcome the problems of the prior art with the use of a precursor unique to the formation of silicon nitride which avoids the problems of plasma deposition, operates at low thermal conditions, avoids Si--C bonds to reduce carbon contamination of the resulting films, has low hydrogen contamination, as well as avoiding chlorine contamination and operates at low pressures (20 mTorr-2 Torr) in a manufacturable batch furnace (100 wafers or more), as will be described in greater detail below.